The present invention relates to a combustion control technique of an internal combustion engine, and particularly, to an ignition control technique for suppressing a variation of combustion pressure for each cycle.
Heretofore, a lean combustion engine has been known in which a mixture having a much leaner air-fuel ratio than a theoretical air-fuel ratio is combusted (refer to Japanese Unexamined Patent Publication No. 9-049452).
When combustion is performed in the vicinity of a lean limit, the combustion becomes unstable, randomly causing cycles where a combustion pressure is high and cycles where the combustion pressure is low.
Therefore, conventionally, there has been caused a problem in that in order to suppress the fluctuation of combustion pressure for each cycle by stabilizing the combustion, a lean limit air-fuel ratio is narrowed toward a rich side.
As disclosed in Japanese Unexamined Patent Publication No. 58-195068, a method has been proposed where the deterioration of combustion is judged so as to re-ignite the engine. However, according to this method, since the deterioration of combustion is judged around the maximal point of combustion pressure, only a misfire is prevented, and the fluctuation of combustion pressure cannot be prevented.
The present invention is aimed at solving the above-mentioned problem, and an object thereof is to enable to reduce the cycle fluctuation of combustion pressure during the combustion performed in the vicinity of a lean limit by an appropriate ignition control, to thereby expand a lean limit air-fuel ratio toward a leaner side.
In order to achieve the above object, the present invention is constituted such that a combustion state is judged soon after the starting of combustion in an initial stage after the ignition, and when an occurrence of incomplete combustion is judged, the re-ignition is performed immediately.
According to this constitution, the combustion property during that combustion stroke is improved at once, and the combustion pressure is sufficiently increased, so that the cycle fluctuation of the combustion pressure during combustion in the vicinity of the lean limit can be reduced to expand the lean limit air-fuel ratio toward the leaner side.
The other objects and features of the present invention will become understood from the following description with reference to the accompanying drawings.